1. Field of the Invention
This invention relates to an improvement in wide angle lenses for use in micrographics to reduce engineering drawings to microimage size upon full exposure with improved resolution and simplicity in the individual lens elements. In one aspect this invention relates to an ultra-wide angle lens using the most desirable glasses and minimizing the thickness and radii of the individual lens elements.
2. Description of the Prior Art
Wide angle lenses for reducing the light path and simplifying micrographic imaging equipment is a continual field of inventive endeavor, and design of such lenses affording improvements in angularity without sacrificing resolution is important as well as placing emphasis on the ease of manufacture of such wide-angle lenses and using glasses which are common, avoiding those which are easily stained, excessively soft, or prone to striae.
The lens of the present invention is comparable to other unsymmetrical wide-angle lenses such as those illustrated and discussed in U.S. Pat. No. 3,997,247 on the basis of performance in that the lens of the current invention also approaches the diffraction limit. The prior art wide angle lens comprises five or six lens groups, a "group" being understood not to necessarily imply a combination of two or more lens elements. The lens of the present invention however differs in that it includes 10 lens elements which are divided into four groups. The first group comprises two meniscus lens elements which are axially separated, the second group comprising an element having a front face which is convex, and the group is provided with converging power, an aperture, a third group of negative power with the third lens element of the group being convex toward the rear of the lens; and the fourth group comprises a cemented doublet.
The lens elements of the present invention use glasses with desirable chemical and mechanical properties and all of the lenses have an axial thickness greater than about 10% of the diameter. Lenses with small radii of curvature are avoided. Also, triplet constructions for the lens elements are avoided. The lens provides wide angular coverage to provide a short light path at reductions of 16X, 24X and 30X.